1. Field of the Invention
The present invention relates to an ion mobility spectrometer and an ion-mobility-spectrometry/mass-spectrometry hybrid spectrometer.
2. Description of the Related Art
The ion mobility spectrometry is widely used for appliances such as a gas detector. Also, in addition to the ion mobility spectrometry, the mass spectrometry exists in ion detection methods. The following clear distinction, however, exists between these two methods, i.e., the ion mobility spectrometry and the mass spectrometry: In the ion mobility spectrometry, the number-of-times of collisions between ions and a gas at the time of the separation is larger in number, and rather, the effect of these collisions is taken advantage of positively. In contrast thereto, in the mass spectrometry, the number-of-times of the collisions between ions and a gas at the time of the separation is smaller in number. Namely, the ion mobility spectrometry is performed under a pressure higher than 10 mTorr; whereas the mass spectrometry is performed under a pressure lower than 1 mTorr. As a result, a significant difference therebetween is as follows: In the ion mobility spectrometry, the separation is performed based on the ion mobility; whereas, in the mass spectrometry, the separation is performed based on mass-to-charge ratios of the ions.
Hereinafter, the explanation will be given below concerning the conventional technologies. In “Analytical Chemistry”, Vol. 66, No. 23, Dec. 1, 1994, pp. 4195 to 4201, the detailed description is given regarding Drift-Tube Ion Mobility Spectrometry (: DTIMS). According to this method, the attainment time of an ion to a detector is represented by the following (Expression 1), assuming that electric field is uniform, and letting ion mobility of the ion be K, voltage be V, and displacement distance be L.
                    T        =                              L            2                    KV                                    (                  Expression          ⁢                                          ⁢          1                )            
Since the value of the ion mobility K differs depending on ion species, it is possible to separate the ion species by using the detector attainment times. The ion mobility spectrometry which takes advantage of the difference in the ion mobility like this is widely used for appliances such as an explosives detector in an airport or the like.
In U.S. Pat. No. 6,498,342 B1, the disclosure is made concerning a method where, after the ions are separated using the ion mobility, the separated ions are further detected by a mass spectrometry unit. According to this method, after the ions are separated using the ion mobility once, the mass spectrometry detection is performed by sequentially introducing the separated ions into the mass spectrometry unit such as a time-of-flight mass spectrometer. Since two-dimensional data (i.e., first-dimensional data: the ion mobility, second-dimensional data: masses of the ions) can be acquired, the resolving power is enhanced significantly.
Moreover, in U.S. Pat. No. 6,774,360 B2, the disclosure is made regarding a method of performing the ion separation by using High-Field Asymmetric-wave form Ion Mobility Spectrometry (: FAIMS). The ion mobility of the ions varies under a high electric-field strength. A filter for permitting a specific ion species to pass therethrough is implementable by using the fact that this variation ratio in the ion mobility differs depending on the ion species. The separation mechanism in U.S. Pat. No. 6,774,360 B2 differs from those in “Analytical Chemistry”, Vol. 66, No. 23, Dec. 1, 1994, pp. 4195 to 4201 and U.S. Pat. No. 6,498,342 B1. This separation mechanism, however, is regarded as one type of the ion mobility spectrometry, since it is a separation mechanism performed under the atmospheric pressure or a low vacuum.